I recently discovered The College Mathematics Journal and enjoyed reading through some of the articles on fun applications of mathematics. I'd like to send some of the articles to my younger sister, a high school sophomore, but unfortunately most of them require calculus, a subject she hasn't studied yet.

Are there any other journals or websites that publish quality articles on applied math that a high school student taking pre-calculus could understand reasonably well?

The most popular resource among the students at the MathPath summer camp seems to be the web site Art of Problem Solving. (I also highly recommend summer camps such as MathPath, although that particular one is for ages 11-14. In my impression, the four most venerated choices at the high school level are MathCamp, Promys, Ross, and Hampshire. It may be challenging to get into these; the AMS maintains an extended list.)

For what it's worth, I don't particularly pay attention to the opportunities available at the high school level, and the four programs you named are the four I've heard of.
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Michael LugoDec 1 '09 at 18:26

These are probably the four that tend to show up in the vitas of mathematicians. Also, reputation always has a degree of self-fulfillment.
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Greg KuperbergDec 1 '09 at 18:33

Mathematical Mayhem was a math journal intended for and run by high school and university students. It now runs as a section within the journal Crux Mathematicorum, published by the Canadian Math Society. It looks like the Math Mayhem section is accessible without a subscription. However, the focus seems to be on problem-solving, so maybe it isn't what you're looking for, but I thought I'd mention it just in case.

The Girls' Angle Bulletin is another great resource with lots of interesting articles about math aimed at a pre-college level. It's especially nice because the style of writing is informal and the articles span a wide variety of mathematical topics. All the past issues are available for free online: http://girlsangle.org/page/bulletin.html

There is a Hungarian mathematics (and physics) journal for high-school students (KöMaL); I think it's mostly in Hungarian, but there are some English articles on their homepage, and there are some special issues in English. They also have running competitions, which are definitely available in English (for the last 40 years or so!). There is an archive of old issues, which seems to contain English material as well, but unfortunately it is not working at the moment...